1. Field of the Invention
The present invention relates to a keyless entry device that performs predetermined control such as unlocking of doors of a vehicle by performing mutual communication between a vehicle-side device and a portable device.
2. Description of the Related Art
In a keyless entry device described in Japanese Unexamined Patent Application Publication No. 2010-185186, in order to prevent relay attack, a vehicle-side device transmits a request signal in which a signal intensity change is changed at a predetermined timing to a portable device, and the portable device detects whether or not there is a change point of signal intensity of the request signal, determines that a signal of which the change point is not detected is a fraudulent request signal, and does not transmit an answer signal.
Here, relay attack is performed by a first relay device arranged near a vehicle and a second relay device arranged at a position separated from the vehicle and performing wireless communication with the first relay device. That is, the first relay device receives an LF signal such as a request signal transmitted from a vehicle-side device near the vehicle, and transmits the signal to the second relay device, and the second relay device transmits an LF signal obtained by reproducing the signal. If a person holding the portable device approaches the second relay device, the portable device receives the LF signal from the second relay device. Here, in response to reception of a signal relayed by the two relay devices, the portable device transmits an answer signal composed of an RF signal. If the vehicle-side device receives this answer signal, the vehicle performs an unlocking operation in a place unintended by a user.
However, in recent years, a fraudulent relay device for relay attack has appeared as being capable of transmitting a request signal with an indication indicating whether or not there is an intensity change. Merely changing the signal intensity at a predetermined timing is insufficient to resolve relay attack.